As is known, in current internal combustion engines, the quantity of fuel actually injected into each cylinder at each injection may differ, even widely, from the nominal fuel quantity calculated by the electronic central control unit controlling injection according to user requirements, and which is currently used to determine the energization time of the injectors.
Various factors account for the difference between the nominal and actually injected fuel quantities, foremost of which are fabrication process spread and time-drift variations in injector characteristics, aging of the injection system, the effect on injection of so-called pressure waves, etc.
The difference between the theoretical and actually injected fuel quantities has extremely negative effects—especially on exhaust gas emission levels, on account of the engine operating at other than the design mixture ratio—and at any rate contributes in aggravating performance spread of engines equipped with this type of injection system.